Method of monitoring the depth of snow

ABSTRACT

A method is disclosed for monitoring the depth of snow with respect to the ground. The method may employ a global positioning system and includes an initialization unit for generating ground surface data representative of the surface of the ground. The method also includes a snow surface data acquisition unit for generating snow surface data representative of the surface of the snow. The method further includes an analysis unit in communication with the ground surface data and the snow surface data for comparing the ground and snow surface data. Snow depth data is then generated representative of the area between the ground and snow surfaces.

This is a divisional of application Ser. No. 08/815,280 filed on Mar.10, 1997 now U.S. Pat. No. 5,761,095.

BACKGROUND OF THE INVENTION

The invention generally relates to systems for monitoring the depth ofsnow, and particularly relates to systems for use at recreational winterresort areas.

Recreational alpine skiing areas typically provide a variety of downhillski trails or pistes on a mountain having a combination of naturaland/or machine made snow. The process of making machine made snow isgenerally expensive as it involves transporting compressed air and waterup a mountain to a series of nozzles distributed along the edge of theski trails. Accordingly, resort areas strive to conserve their financialresources and make snow only in places where it is most needed.Decisions regarding the optimal placement and use of snow makingequipment as well as the distribution of snow on a ski trail via snowgrooming vehicles having plows, are sometimes extremely important,particularly when the amount of natural snow is very low. It isgenerally desirable to ensure a fresh, soft snow surface on as manytrails as possible to provide the skier with a pleasurable skiingexperience. The resort operator is typically interested in ensuring thatskier traffic, melting of snow or wind scouring of the snow surface donot expose the ground. Also, it is desirable that snow coverage remainas complete as possible for as long as possible through the ski season.

There is a need, therefore, for resort operators to have snow depthinformation available throughout the season to facilitate the efficientuse of snow making and snow grooming equipment.

SUMMARY OF THE INVENTION

The invention provides a system for monitoring the depth of snow withrespect to the ground. The system includes a global positioning system(GPS) for generating ground surface data representative of the surfaceof the ground, and snow surface data representative of the surface ofthe snow. The system further includes an analysis unit in communicationwith the ground surface data and the snow surface data for comparing theground and snow surface data. Snow depth data is then generatedrepresentative of the area between the ground and snow surfaces. In oneembodiment, individually measured points on the ground surface and thesnow surface are used to develop an approximated surface model of theground and snow surfaces. The ground surface points may be recorded bymounting a GPS receiver on a tractor mower when there is no snow on theground, and the snow surface points may be recorded during the winter bymounting a GPS receiver on snow grooming equipment.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description of the illustrated embodiments may befurther understood with reference to the accompanying drawings in which:

FIG. 1 is a functional block diagram representative of a system of theinvention;

FIG. 2 is a diagrammatic representation of the equipment used forinitialization of the system of FIG. 1;

FIG. 3 is a diagrammatic representation of the equipment used foroperation of the system of FIG. 1;

FIG. 4 is a flow chart showing the steps performed during the datacollection process for initialization and operation;

FIG. 5A is a diagrammatic graphical representation of surface datacollected in accordance with the process of FIG. 4;

FIGS. 5B-5D are diagrammatic graphical representations of surface modelsgenerated in accordance with the process of FIG. 4; and

FIG. 6 is functional block diagram of another embodiment of theinvention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

With reference initially to FIG. 1, a system of the invention includes areal time kinematic (RTK), global position system (GPS) with on-the-fly(OTF) capability and National Marine Engineering Association (NMEA)output. A suitable GPS system is the Trimble 4400 model RTK system soldby Trimble Navigation Limited. of Sunnyvale, Calif. which providesaccuracy of about 1 cm. As shown in FIG. 1, the GPS system includes anRTK base unit 10 and an RTK rover unit 12. The RTK base unit 10 includesa satellite receiver antenna 14 in communication with an RTK GPS basereceiver and processor 16, and further includes a radio frequency (RF)Tx radio modem transmit antenna 18 in communication with an RF signaltransmitter unit 20. The RTK base unit 10 is positioned at a fixedlocation having known longitude, latitude and elevation coordinates. Asuitable location for the base unit 10 may be a building on an alpineski resort mountain, preferably an exposed building that is on themountain itself rather than one at the base of the mountain.

The RTK rover unit 12 includes a satellite receiver antenna 28 incommunication with an RTK GPS rover receiver and processor 30, andfurther includes an RF Rx radio modem receiver antenna 24 incommunication with an RF signal receiver unit 26. The RTK rover unit 12also includes a data input/output (I/O) device 32, from which data maybe periodically transferred to another location such as anadministrative office 34, via e.g., electronic transfer, RF signaltransfer, or manual transfer of a data diskette. The RTK rover unit 12is preferably located within a tractor used for snow groomingoperations.

Generally, during operation, satellite signals are continuously receivedfrom the available satellites 36 by the receiver antennas 14 and 28. Thelongitude, latitude, and elevation of the base unit 10 are known, andare compared with the signals received from the satellites by theantenna 14. The difference between the received and pre-recorded knowndata is used to correct the information received by the rover unit 12.This difference is communicated to the rover unit 12 by RF signaltransmission from the RF signal transmitter 20 and antenna 18 to the RFsignal receiver 26 and antenna 24. Optionally, the system may include aradio digipeter or repeater 38, to retransmit the RF signals transmittedfrom the base to areas of the mountain not reachable by the RF signaltransmitter 20 alone.

Surface model information may thereby be obtained representative of thesurface of the snow at every location covered by the snow groomingtractor. This snow surface data may then be compared with pre-recordedsurface data representative of the surface of the ground without snow.The difference between the surfaces represents the volume of snow on aparticular skiing trail.

As shown in FIG. 2, initialization data representative of the groundsurface may be acquired by employing, for example, a grass mowingtractor 40 during a time of year when there is no snow on the ground tomap the surface of the ground 46. The tractor 40 includes an RTK roverunit having an RF signal receiver antenna 42 and a satellite receiverantenna 44 similar to the antennas 24 and 28 shown in FIG. 1. Thecollected data is corrected by the correction data from an RTK base unit10 as discussed above, and the distance h, between the ground and theheight of the antenna 44 is subtracted from the measured elevation. Agrid map of the surface of the ground is thereby generated as shown at52 in FIG. 5A, with each point on the grid (in x-y-z coordinates) beingrepresentative of a measured set of longitude, latitude and elevationdata for a particular point on the surface of the ground. In otherembodiments, the ground surface data may be compiled from a variety ofsources, such as satellite imaging, radar imaging, aerial photography,stereophotography, analysis of contour maps, and reviewing other publicrecords.

In the present embodiment, the development of the ground surface modelis conducted during the time of year when there is no snow on theground, preferably in the early spring or late fall when deciduous treeshave shed their leaves, providing a better opportunity for satellitedata collection. Ski resorts traditionally mow their ski trails in latesummer and fall, providing an excellent opportunity to utilize existingmanpower and equipment for the data collection process. As the GPS unitis maneuvered over the ground surface, the base elevation data iscollected. This process need only be conducted once, as the groundsurface is not likely to change over a long period of time. Datacollection should be complete and cover all portions of the ski trail toensure maximum accuracy. Satellite availability coordination is criticalto the development of the data collection process. This can befacilitated through use of the Trimble 4400 software which provides adaily forecast of satellite availability and position information.

As shown in FIG. 4, the initialization process for generating the groundsurface model begins (step 400) with the collection of data by the RTKrover unit in the tractor 40 (step 405). Data is generated for a pointevery second, and recorded in NMEA format until the period for recordingdata is complete (step 410). The period for collecting the data may be,for example, a week or a month. The recorded data is then transferred(step 420) to the administrative office 34 as shown in FIG. 1 where itis stored as a text file.

The NMEA text file includes projection information, time, date,latitude, longitude, elevation, signal quality, number of satellitesobserved, percentage of precipitation dilution, and units of measure.The quality of the signal is of significant importance and it ispreferred that only signals meeting a minimum quality threshold be used,e.g., signals received from 3 or more satellites.

The data file is then processed (step 430) and converted to aselectively edited file that includes a series of x-y-z coordinates.This step includes purging data that was recorded when the quality ofthe signal was low, and elimination of NMEA data that is unused, e.g.,time, date etc. This edited text file is then converted (step 440) to aground surface model file by modeling software such as, for example,QUICKSURF sold by Schreiber Instruments, Inc. of Denver, Colo., SURVEYCOMPLETE sold by Softdesk, Inc. of Henniker, N.H., or SITEWORKS sold byIntergraph Corporation of Huntsville, Md. The data is then reviewed(step 450) to ensure that the data points are within the defined skitrails. The administrator may elect the output option of his or herchoice for the ground surface model file 50 which includes, e.g., a gridas shown at 54 in FIG. 5B, a contour mapping as shown at 56 in FIG. 5C,or a triangulated integer network (TIN) as shown at 58 in FIG. 5D.

Once the ground surface model is imported to the surface modelingsoftware during initialization, the outline of the ski trails or trailsections should be defined by a computer aided design (CAD) closedpolyline to capture all relevant data points within the boundary of thepolylines. The ground surface model file should then be thoroughlyreviewed (step 460) to ensure that there are no significant areas voidof geographic point data. In the event a void area does exist, such asareas where there is no grass to be mowed, additional data collection inthe void area should be conducted and the data collected should be addedto the initialization file.

When the ground data collection process is finished and the ski trailshave been completely mapped, the ground surface data is converted (step470) to drawing file format, e.g., a drawing exchange file (DXF), anAutocad file (DWG), or Microstation file (DGN). The drawing file is thentransferred to a geographical interface (GIS) or CAD system. The filemay also be transferred to various other software and/or hardware suchas a network server, a video display or a printer.

As shown in FIG. 3, during operation in the winter, surface data isgenerated by employing a snow grooming tractor 48 including an RTK roverunit 12 having an RF receiver antenna 24 and a satellite receiverantenna 28. Again, the collected data is corrected by the correctiondata from an RTK base unit, and the distance h₂ between the ground andthe height of the antenna 28 is subtracted from the measured elevation.A map 60 of the surface of the snow is thereby generated, with each datapoint (in x-y-z coordinates) being representative of a measured set oflongitude, latitude and elevation data for a particular point on thesurface of the snow. The volume indicated at d and extending across thearea of the ski trail, may be calculated from the snow surface data mapand the ground surface data map.

Operational data collection is commenced (step 480) when theadministrator desires and when sufficient snow is present to providesnow surface data collection opportunity. Data collection (step 490) isconducted as generally discussed above in connection with FIGS. 1 and 3by maneuvering the RTK GPS rover unit over the snow surface until theend of the data collection period (step 500). The data collection can bedone by a skier, by walking, by snow mobile, by all-terrain-vehicle, orby snow grooming equipment. It is believed to be efficient to utilizethe snow grooming vehicles during their normal snow grooming operations.Ski resorts generally groom their trails after the close of operationeach day and frequently operate through the night until the ski areaopens in the morning. The data collection process by snow groomingvehicle is done without modification of the normal grooming operations,and is generally an activity that can be easily performed by the vehicleoperator.

The operational data collection process is conducted as theadministrator deems necessary, but generally it is recommended to bedone daily. The ski resort may equip one or many vehicles with thenecessary RTK GPS equipment, and coordinate the grooming activities tocorrespond with the desired trails to be modeled.

The data collection is done as the grooming is performed and unlikeduring initialization, the data is fully processed and converted to adrawing file (steps 420, 430, 440, and 470) irrespective of whether voidareas exist in the surface model. If void areas exist, the system maydesignate the trails for which the data is incomplete as havinginsufficient data. The data for that trail may either be used togenerate snow depth data, or may be ignored until a data collection teamis able to generate a complementary set of data to complete the file.The processing of the text file and purging of the data for poor qualitysatellite signals is done as discussed above in connection with theinitialization process.

The map 60 of the snow surface is then converted to a grid pattern asshown at 62 in FIG. 5B, a contour mapping as shown at 64 in FIG. 5C, ora TIN pattern as shown at 66 in FIG. 5D by interpolating the necessarydata points from the non-uniform set of measured data in the map 60similar to the generation of surfaces 54,56 and 58 from the non-uniformground surface data 52.

The surface modeling software then combines the snow surface model datawith the ground surface model data in a graphical representation. Thevolume of snow is determined by developing a snow depth model, which iscalculated by the surface modeling software. Again, the file outputformat may be, for example, grid, TIN, or contour, etc. at thediscretion of the system administrator. The snow depth model is computedby calculating the difference between the initialization model and thesnow surface model. The model is output in a file configurationcompatible with the CAD or GIS system format (e.g., DXF, DWG, or DGN)used by the administrator. In alternative embodiments, the output filemay include a plan view of each ski trail in multiple colors with eachcolor representing a different range of snow depth. The snow depth fileis available for printing, viewing or manipulating after the compilationhas been completed, and may be stored for later review.

As shown in FIG. 6, an alternative embodiment of a system of theinvention includes an RTK base unit 80 positioned at a fixed location,and including a satellite antenna 82 and an RTK base receiver 84. Thebase unit 80 also includes an RF transmitter 86 and an RF transmitterantenna 88. The system further includes a plurality of RTK rover unitspositioned in snow grooming tractors 90, each of which also includes asatellite receiver 92, an RTK rover unit 94, an RF transmitter 96, andan RF transmitter antenna 98.

In this system, the signals from the satellites 100 that are received bythe receivers in the roving units 92 are sent directly via RFtransmission, without processing or editing, to a central station suchas an administrative office 102. In such a system, all of the datafiltering and processing is performed at the office 102. The base unitoperates as it does in the system as disclosed above with reference toFIG. 1, with the exception that the signal is received at the base asopposed to the roving units. This system permits each rover unit toinclude much less equipment, and avoids the need to have dataperiodically downloaded from the snow grooming equipment.

Those skilled in the art will appreciate that numerous modifications andvariations may be made to the above disclosed embodiments withoutdeparting from the spirit and scope of the invention.

I claim:
 1. A method of monitoring the depth of snow with respect to theground, said method comprising the steps of:generating ground surfacedata representative of the surface of a section of ground; generatingsnow surface data representative of the surface of the snow on saidsection of ground; and comparing said ground surface data and said snowsurface data and generating data representative of the snow depthbetween said ground and snow surfaces.
 2. A method as claimed in claim1, wherein said method further includes the step of displaying said snowdepth data.
 3. A method as claimed in claim 1, wherein said step ofgenerating snow surface data includes the step of receiving radiotransmission signals from a plurality of satellites.
 4. A method asclaimed in claim 3, wherein said step of generating snow surface dataincludes the steps of identifying and filtering unreliable data from thesatellites.
 5. A method as claimed in claim 1, wherein said step ofgenerating snow surface data includes the step of generating referencedata representative of the difference between known position data andmeasured position data, and the step of correcting said generated snowsurface data by said reference data.
 6. A method of monitoring the depthof snow with respect to the ground at an alpine ski resort, said methodcomprising the steps of:generating three dimensional ground surface datarepresentative of the surface of a section of ground; generating threedimensional snow surface data representative of the surface of the snowon said section of ground using a global positioning system; andidentifying and removing unreliable data from said snow surface data;and displaying said ground surface data and said snow surface data.
 7. Amethod as claimed in claim 6, wherein said step of generating snowsurface data includes the step of approximating said three dimensionalsnow surface data by interpolating between actually measured datapoints.
 8. A method of monitoring the depth of snow with respect to theground, said method comprising the steps of:generating ground surfacedata, said ground surface data including ground surface data points eachof which is representative of the longitude, latitude and elevation of apoint on the surface of a section of ground; generating snow surfacedata, said snow surface data including snow surface data points each ofwhich is representative of the longitude, latitude and elevation of apoint on the surface of the snow on said section of ground; generatingground surface model data representative of the surface of said groundfrom said ground surface data, and generating snow surface model datarepresentative of the surface of said snow from said snow surface data;and comparing said ground surface model data with said snow surfacemodel data, and generating data representative of the snow depth betweensaid ground and snow surfaces.